The presence and activity of enzymes can be used to determine the health or metabolic state of a cell. Enzymes can also be markers for a particular cell type since the occurrence and activity of certain enzymes is frequently characteristic of a particular cell. For instance, the activity of certain enzymes can often be used to distinguish cells of bacterial, plant or animal origin or to distinguish the identity of tissue from which the enzyme originates.
Glycosidases, also know as glycoside hydrolases, catalyze the hydrolysis of the glycosidic linkage to generate two smaller sugars. They are extremely common enzymes with roles in nature including degradation of biomass such as cellulose and hemicellulose, in anti-bacterial defense strategies (e.g. lysozyme), in pathogenesis mechanisms (e.g., viral neuraminidases) and in normal cellular function (e.g. trimming mannosidases involved in N-linked glycoprotein biosynthesis). In bacteria and prokaryotes, glycosidases are found both as intracellular and extracellular enzymes that are largely involved in nutrient acquisition. One of the important occurrences of glycosidases in bacteria is the enzyme beta-galactosidase (LacZ), which is involved in the regulation of expression of the lac operon in E. coli. In higher organisms, glycosidases are found within the endoplasmic reticulum and Golgi apparatus where they are involved in processing of N-linked glycoproteins, and in the lysozome as enzymes involved in the degradation of carbohydrate structures. Deficiency in specific lysosome glycosidases can lead to a range of lysosomal storage disorders that result in development problems or death. Glycosidases are involved in the biosynthesis and degradation of glycogen in the body. Together with glycosyltransferases, glycosidases form the major catalytic machinery for the synthesis and breakage of glycosidic bonds.
Diaphorases are a ubiquitous class of flavin-bound enzymes that catalyze the reduction of various compounds, which act as hydrogen acceptors, from the reduced form of di- and triphosphopyridine nucleotides, i.e., NADH, NADPH. Cellular energy metabolism is a complex process that allows cells to store energy through a series of enzymatic and chemical reactions. One essential aspect of cellular energy metabolism is the reduction-oxidation state of the cell. The metabolic status of live cells as well as the assaying of enzyme activity and/or metabolite level can be determined by measuring the redox defining co-factor NAD(P)/NAD(P)H.